1. Field of the Invention
The present invention relates generally to compounds, compositions and methods regulating the actions of androgens and other steroid hormones by modulating the activity of 5.alpha.-reductase. More particularly, the present invention relates to the use of these compounds to treat disorders that are caused by abnormal androgen action in cells or organs. This invention also deals with the use of natural and synthetic fatty acids and catechins, especially polyunsaturated fatty acids and their derivatives and epigallocatechin gallates, as 5.alpha.-reductase inhibitors and as therapeutic agents.
2. Description of the Related Art
Uses of androgens known to the medical arts include, for example, treatment of hypogonadism and anemia (Synder, 1984; Mooradian et al., 1987). The abuse of androgen among athletes to enhance performance is well known (Strauss and Yesalis, 1991). Androgens are also known to promote the development of benign prostatic hyperplasia (BPH) (Wilson, 1980), prostate cancer (Huggins and Hodges, 1940), baldness (Hamilton, 1942), acne (Pochi, 1990), hirsutism, and seborrhea (Hammerstein et al., 1983; Moguilewslcy and Bouton, 1988). Approximately 70% of males in the U.S. over the age of 50 have pathological evidence of BPH (Carter and Coffey, 1990). Prostate cancer is the second leading cause of cancer death in males in the U.S. (Silverberg and Lubera, 1990; Gittes, 1991). Male-patterned baldness can start as early as the teens in genetically susceptible males, and it has been estimated to be present in 30% of Caucasian males at age 30, 40% of Caucasian males at age 40, and 50% of Caucasian males at age 50. Acne is the most common skin disorder treated by physicians (Pochi, 1990) and affects at least 85% of teenagers. In women, hirsutism is one of the hallmarks of excessive androgen action (Ehrmann and Rosenfield, 1990). The ovaries and the adrenals are the major sources of androgen in women.
1. Differential Actions of Testosterone and 5.alpha.-Dihydrotestosterone (5.alpha.-DHT) PA1 2. Biological Importance of 5.alpha.-Reductase PA1 3. Steroidal 5.alpha.-Reductase Inhibitors PA1 4. Biological and Biochemical Effects of Fatty Acids and Lipids
In men, the major androgen circulating in the blood is testosterone. About 98% of the testosterone in blood is bound to serum proteins (high affinity binding to sex-steroid binding globulin and low affinity binding to albumin), with only 1-2% in free form (Liao and Fang, 1969). The albumin-bound testosterone, the binding of which is readily reversible, and the free form are considered to be bioavailable, and account for about 50% of total testosterone. Testosterone enters target cells apparently by diffusion. In the prostate, seminal vesicles, skin, and some other target organs it is converted by a NADPH-dependent 5.alpha.-reductase to a more active metabolite, 5.alpha.-DHT. 5.alpha.-DHT then binds to androgen receptor (AR) in target organs (Anderson and Liao, 1968; Bruchovsky and Wilson, 1968; Liao, 1975). The 5.alpha.-DHT-receptor complexes interact with specific portions of the genome to regulate gene activities (Liao et al., 1989). Testosterone appears to bind to the same AR, but it has a lower affinity than 5.alpha.-DHT. In tissues such as muscle and testes, where 5.alpha.-reductase activity is low, testosterone may be the more active androgen.
The difference between testosterone and 5.alpha.-DHT activity in different androgen-responsive tissues is further suggested by findings in patients with 5.alpha.-reductase deficiency. Males with 5.alpha.-reductase deficiency are born with female-like external genitalia. When they reach puberty, their plasma levels of testosterone are normal or slightly elevated. Their muscle growth accelerates, the penis enlarges, voice deepens, and libido toward females develops. However, their prostates remain non-palpable, they have reduced body hair, and they do not develop acne or baldness. Females with 5.alpha.-reductase deficiency do not have clinical symptoms (Imperato-McGinley, 1986).
The findings in 5.alpha.-reductase deficient patients suggest that inhibitors of 5.alpha.-reductase would be useful for the treatment of prostatic cancer, BPH, acne, baldness, and female hirsutism. Clinical observations and animal experiments have indicated that spermatogenesis, maintenance of libido, sexual behavior, and feed-back inhibition of gonadotropin secretion do not require the conversion of testosterone to 5.alpha.-DHT (Brooks et al., 1982; Blohm et al., 1986; George et al., 1989). This is in contrast to other hormonal therapies which abolish the actions of both testosterone and 5.alpha.-DHT.
Treatments of androgen-dependent skin and prostatic diseases by 5.alpha.-reductase inhibitors would be expected to produce fewer side effects than the presently available hormonal therapies. These include castration, estrogen therapy, high doses of superactive gonadotropin-releasing hormone such as Luprolide, and the use of competitive antiandrogens which inhibit AR binding of testosterone and 5.alpha.-DHT, such as flutamide, cyproterone acetate and spironolactone. The long term efficacy of `competitive antiandrogens` is also compromised by their block of the androgenic feedback inhibition of gonadotropin secretion. This results in elevated gonadotropin secretion, which in turn increases testicular secretion of testosterone. The higher level of testosterone eventually overcomes the action of the antiandrogen.
Excessive 5.alpha.-DHT is implicated in certain androgen-dependent pathological conditions including BPH, acne, male-pattern baldness, and female idiopathic hirsutism. It has been shown that 5.alpha.-reductase activity and the 5.alpha.-DHT level are higher in the presence of BPH prostates than that of the patients with normal prostates (Isaacs, 1983; Siiteri and Wilson, 1970). 5.alpha.-reductase activity is reported to be higher in hair follicles from the scalp of balding men than that of nonbalding men (Schweikert and Wilson, 1974).
The most potent inhibitors of 5.alpha.-reductase developed so far are steroids or their derivatives. Among these the 4-azasteroidal compounds (Merck Co.) are the most extensively studied (Liang et al., 1983; Rasmusson et al., 1986). These inhibitors are 3-oxo-4-aza-5.alpha.-steroids with a bulky functional group at the 17.beta.-position, and act by reversibly competing with testosterone for the binding site on the enzyme.
The A-ring conformation of these compounds is thought to be similar to the presumed 3-enol transition state of the 5.alpha.-reduction of 3-oxo-.DELTA..sup.4 -steroids. A prototype for 5.alpha.-reductase inhibitors is 17.beta.-N,N-diethylcarbamoyl-4-methyl-4-aza-5.alpha.-androstan-3-one (4-MA), which behaves as an inhibitor of 5.alpha.-reductase in vivo, decreasing the prostatic concentration of 5.alpha.-DHT in intact male rats or in castrated male rats given testosterone propionate. 4-MA attenuated the growth of the prostate of castrated rats induced by testosterone, but had much less of an effect in rats given 5.alpha.-DHT (Brooks et al., 1981).
When dogs are treated with 4-MA, the prostate size decreases (Brooks et al., 1982; Wenderoth and George, 1983). Topical applications of 4-MA to the scalp of the stamptail macaque, a primate model of human male pattern baldness, also prevented the baldness which normally occurs at puberty in these monkeys (Rittmaster et al., 1987). These results also suggest that the growth of the prostate in rats and dogs, and baldness in the stamptail macaque depend on 5.alpha.-DHT. On the other hand, studies in rat pituitary cultures showed that complete inhibition of testosterone conversion to 5.alpha.-DHT by 4-MA did not affect testosterone inhibition of LH release, indicating direct action of testosterone in this system (Liang et al., 1984).
Another potent inhibitor is Proscar.TM. (Merck Co.) (Finasteride, MK-906, or 17.beta.-N-t-butylcarbamoyl-4-aza-5.alpha.-androst-1-en-3-one). The inhibitor has no significant affinity for the rat prostate AR. In clinical trials, Proscar.TM. decreases the plasma level of 5.alpha.-DHT and the size of the prostate and also improves urinary flow in patients with benign prostatic hyperplasia (Vermeulen et at., 1989; Rittmaster et al., 1989; Gormley et al., 1990; Imperato-McGinley et al., 1990). In stamptail macaque monkeys, Proscar.TM. administered orally at 0.5 mg/day, alone or in combination with topical 2% Minoxidil.TM., reduced serum 5.alpha.-DHT level, and reversed the balding process by enhancing hair regrowth by topical Minoxidil.TM. (Diani et al., 1992). The effects of Minoxidil.TM. and Proscar.TM. were additive.
Among other steroidal compounds shown to inhibit 5.alpha.-reductase are 4-androstane-3-one-17.beta.-carboxylic acid (Voigt et al., 1985), 4-diazo-21-hydroxymethyl-pregnane-3-one (Blohm et al., 1989), and 3-carboxy A-ring aryl steroids (Brandt et at., 1990).
Since treatments of androgen-dependent skin and prostatic diseases by 5.alpha.-reductase inhibitors can produce fewer side effects than the hormonal therapies which indiscriminately inhibit all androgen actions, it is desirable to provide different types of 5.alpha.-reductase inhibitors.
Several membrane-associated enzymes (e.g., 5'-nucleotidase, acetyl CoA carboxylase) have been shown to be affected by the polyunsaturated fatty acid content of dietary fat, and to alter the physicochemical properties of cellular membranes (Zuniga et al., 1989; Szepsesi et al., 1989). Various types of phospholipases in rat ventricular myocytes are modulated differentially by different unsaturated fatty acids in the culture media (Nalboone et al., 1990). In addition, treatment of cerebral cortical slices (Baba et al., 1984) or intact retina (Tesoriere et al., 1988) with unsaturated fatty acids can enhance adenyl cyclase activities.
Few studies have been directed to the elucidation of the mode of action of free fatty acids on enzymes in cell-free systems. Certain cis-unsaturated fatty acids, at 50 .mu.M, were shown to stimulate protein kinase C activity (Dell and Severson, 1989; Khan et al., 1991) and to inhibit steroid binding to receptors for androgens, estrogens, glucocorticoids, and progestins (Vallette et al., 1988; Kato, 1989). It has not been shown that unsaturated fatty acids can affect steroid receptor binding of steroid hormones in vivo in an animal or human.